1. Field of the Invention
The present invention relates to a photosynthesis reactor tank assembly, and more particularly to a sealed double-tank assembly having an inner tank and an outer tank.
2. Prior Art
The prior art methods for artificially cultivating green algae of the photosynthesized type, particularly such as chlorella, may generally be classified into two type of processes: (1) the composite process in which the culture is grown in an outdoor pool by introducing a supply of organic acids, such as acetic acid, as the carbon source followed by applicaton of natural light, and (2) the autotrophic process in which the culture is grown in a tank by introducing glucose as the carbon source without application of light. Chlorella cultivated by the latter process has a protein composition substantially poorer than that of chlorella cultivated by the former process and is noticeably poorer in terms of yielding substances which promote microbic growth and cell-activating substances, referred to as physiologically active substances of chlorella. Thus, it is obvious that the culture of chlorella is preferably conducted with the application of light.
The composite process, however, has various drawbacks such that (1) the culture fluid may be contaminated with bacteria and the like contained in the atmosphere and the rainwater, (2) culture conditions are dictated by the weather, (3) a relatively large area is required to hold the culture fluid, the depth of which must be limited to less than 30 centimeters for a uniform light application, (4) utilization of carbon dioxide as a nutrient source is relatively low, (5) automatic control of the culture is very difficult, and (6) erosion of a culture pool may lead to deterioration of chlorella.
According to a most commonly used process, the chlorella culture fluid base substantially consists of inorganic salts and, even when urea is used as a nitrogen source, a noticeable amount of bacteria is detected. Furthermore, the chlorella culture fluid of such type may often be contaminated with heavy metals or the like contained in the rainwater which has passed through the contaminated atmosphere. Although the amount of bacteria may be reduced under heat treatment by such means as a plate heater, this treatment may also reduce nutritive qualities or desired effects of chlorella. In addition, it is practically impossible to remove heavy metal contaminants. During the night, photosynthesis will not progress without light and the growth of effective ingredients is also reduced, since the atmospheric temperature becomes lower than in the daytime, whereby the organic ingredients previously synthesized in the daytime may be consumed and the growth of chlorella is suppressed. Additionally, in order to prevent chlorella from perishing, air supply must be maintained by agitation even during the night, which would be uneconomical. The light application in the daytime varies dependent upon the weather and season and a continuous light application on the other hand would deteriorate the growth speed, the carbon utilization rate and the light energy utilization rate of chlorella, even when the amount of light to be applied may be appropriate.
To improve these adverse factors, the light application should be effected intermittently. Although a large pool may be constructed to achieve uniform application of light to the culture fluid, such a large pool increases cost, is readily contaminated with the atmosphere and the rainwater, and makes the agitation of the culture fluid difficult. As the utilization rate of carbon dioxide is too low to be practically used as the carbon source in the culture pool, acetic acid of high purity is used. However, this is very expensive. Although acetic acid may be replaced by substances such as glucose, fructose, mannose and maltose, these substances may facilitate growth of bacteria and thereby suppress the growth of chlorella. If these substances are used, the culture fluid once used cannot be repeatedly used. In addition, since chlorella may perish at pH less than 6, a very strict pH control is required around pH6.
The process mentioned above requires an examination and recording of atmospheric temperature, water temperature, pH value, PCV value, water depth, ratio of dead cells, degree of contamination, amount of sunshine, amount of rainfall and dry weight of algae several times daily for quality control, all of which makes automatic control expensive and difficult. In view of the fact that most culture pools are those of concrete, lixivium likely resulting from possible erosion of the concrete surface thereof enters into the bodies of chlorella, deteriorating the quality thereof, and causing them to die. The dead cells of clorella will emit an offensive odor. This requires frequent cleaning of the culture pool.